Ever expanding mobile communications require increasingly sophisticated antenna technology. The need for antennas capable of operating at multiple bands is continually increasing. Two options exist to meet this needxe2x80x94multiple antennas or multiple-band antennas. Several multiple-band antennas have been developed, but all suffer drawbacks.
The quarter-wave monopole is currently the most popular mobile antenna. A monopole can be a dual-band antenna if it includes a coil or xe2x80x9cchokexe2x80x9d along its length. The monopole antenna with the choke provides dual-band functionality. However, the monopole antenna has drawbacks. First, it is aesthetically undesirable. Second, because it must extend from an exterior portion of the car, it is subject to damage and theft, as well as being a nuisance in going through carwashes.
Another dual-band antenna is the xe2x80x9cAndrewxe2x80x9d antenna, which has a xe2x80x9cbow tiexe2x80x9d configuration. This antenna also has drawbacks. First, it must be mounted inside the car, which reduces its performance well below the performance of a quarter-wave monopole. Second, it does not possess the omnidirectionality required for mobile communication applications.
The planar inverted F antenna (also know as a U-shape or an L-shape) is a single-band, low-profile antenna that provides performance comparable to a quarter-wave monopole. The low profile enables the antenna to be quite unobtrusive, even on a vehicle exterior. However, to handle multiple bands, multiple single-band antennas must be used.
The aforementioned problems are overcome in the present invention comprising a dual-band antenna having an extremely low profile and being relatively compact. Specifically, the antenna includes a ground plane and upper and lower planar elements all parallel to one another and spaced from one another. The lower element is connected to the ground plane through a plurality of shorting posts. A probe or lead interconnects the centers of the upper and lower elements to provide an antenna lead. The lower element alone is responsive to a first frequency band (the higher frequency band); and the coupled upper and lower elements are responsive to a second frequency band (the lower frequency band).
The present antenna has an extremely low profile and is highly compact. It is well suited for mounting in a wide variety of locations inside or outside of a vehicle.
These and other objects, advantages, and features of the invention will be more fully understood and appreciated by reference to the detailed description of the preferred embodiment and the drawings.